The present invention relates to a method for inoculating or refining metal melts by the addition of additives which are introduced into the metal melts by means of high kinetic energy.
In order to positively produce certain characteristics in metals or metal alloys, appropriate additives, elements or alloys are added to such melts, preferably directly preceding casting. For example, cast iron melts are treated with magnesium and/or inoculants to produce spherical graphite or certain structural characteristics, respectively. Aluminum-silicon alloys are refined by the addition of sodium, and steel melts are deoxidized or desulfured by means of additives.
According to presently practiced methods, the substances to be introduced for this purpose are usually added to the melts in pulverized or granular form in the furnace, in the casting pan or in the casting stream, preferably immediately preceding the actual casting. In this connection it is important that these additives are received in the correct quantities, as uniformly distributed as possible, and with low losses so as to avoid wasting the usually expensive additives by the use of excess quantities, melting losses, evaporation losses or floating. At the same time the presence of an air atmosphere may be a drawback in certain cases.
The problems encountered in the production of castings containing spheres of one component, such as graphite, during treatment with the very volatile and oxidizable magnesium are known in practice. For that reason, magnesium is presently added to cast iron melts usually in pressurized pans or special converters. The special equipment required for this purpose, however, involve new investment costs, and a long and costly time period expires between treatment and casting. If, on the other hand, elemental magnesium or pre-alloyed magnesium are added directly to the melts in solid form, there exists the danger, in addition to melting and evaporation losses, that the magnesium, on the one hand, if added in a finely pulverized form, is not sufficiently bound by the melt, while, on the other hand, if it is added in coarser grains, the magnesium may be unable to completely mix with the melt in the time remaining before solidification so that undesirable increases in concentration develop while other parts remain untreated. At the same time, the initially inflowing cast iron still comes into contact with cold magnesium which will not completely dissolve and thus the cast iron flows essentially untreated into the mold where it then solidifies. In particular, small cast pieces weighing up to one kilogram will then no longer have the required characteristics. The above-described drawback in the production of such castings applies in principle more or less also for the inoculation or refinement of cast iron or other metal melts depending on the physical and chemical properties of the additives, regardless of whether the treatment takes place in the furnace, in the pan, or in the casting stream by introduction of the substances in rod or powder form.
It has been proposed, for example, according to German Pat. No. 1,092,496 to overcome the above-described problems by adding magnesium or magnesium alloys, respectively, possibly together with the conventional inoculants in solid form by means of, for example, a blow tube and with the use of a carrier gas and to blow it onto the bath surface of cast iron melts. Although in this case, the additives, due to their increased kinetic energy, will be propelled to below the bath surface and a possibly inert carrier gas prevents melting losses, the proposal of the German patent requires that the additives melt and optimum mixing occurs only as a result of stirring the treated cast iron melt in pressure chambers or pressure pans. This process, in particular, requires additional equipment and the treatment connot be effected, as required for optimum effect, immediately before casting into the mold.